For communication between devices, for example in automotive applications, various protocols are used. One protocol frequently employed is the SENT protocol (single edge nibble transmission). This protocol may for example be used in applications where high resolution data is transmitted for example from a sensor device to an electronic control unit (ECU).
The SPC protocol (short PWM code; PWM meaning pulse width modulation) is an extension of the SENT protocol and aims at increasing performance of a communication link and reducing system costs at the same time. To some extent, SPC allows bidirectional communication and is an example of an edge based PWM protocol. For example, SPC may introduce a half-duplex synchronous communication. A receiver (e.g. master) generates for example a master trigger pulse on a communication line by pulling it low for a defined amount of time. The pulse width (corresponding to the defined amount of time) is measured by a transmitter (e.g. slave), for example a sensor, and a transmission, e.g. a SENT transmission, is initiated only if the pulse width is within a defined limit. The SPC protocol allows choosing between various protocol modes. For example, a synchronous mode, a synchronous mode with range selection or a synchronous transmission with identification (ID) selection (also referred to as busmode), where up to four sensors may be connected in parallel to an ECU or other master device, may be used. In the latter case, the pulse width of the above-mentioned trigger pulse conventionally may define which sensor or other entity will start a transmission. For example, a length of the trigger pulse may indicate an ID of a sensor or other slave device selected for transmission. The sensor or other entity may start the transmission with its own synchronization, which may overlap the trigger pulse.
Conventionally, when using the SPC protocol in the above-mentioned busmode, each sensor may have a different length of the trigger pulse associated therewith. In the conventional SPC protocol, triggering a sensor by a trigger pulse has a comparatively long duration (for example about 90 time units for addressing, e.g. the trigger pulse, and at least about 281 time units for responding of the sensor) and therefore takes a comparatively long time. Additionally, between triggering of different sensors in some conventional approaches at least the longest possible transmission duration plus a safety margin has to be kept.
Further, conventional approaches attempting to reduce the time needed are disclosed in US 2015/0236876 A1 or US 2016/0050089 A1.
Some conventional approaches may require a slave device to “listen” to the bus all the time and detect transmissions from other slave devices and their termination. This may require comparatively complex receive hardware and/or logic in slave devices, which may be undesirable.